Epitaxial nucleation of crystallization at polymer-filler interfaces

In polymer composites the interaction between polymer matrix and filler par ticles often results in nucleation of spherulites. The principles of polyme r crystal nucleation and spherulite growth are investigated using scanning transmission electron microscopy (STEM) and microdiffraction techniques in combination with polarized light microscopy. Simultaneous diffraction patte rns from the interface of the filler and the polymer were obtained, Special precautions for successful recording of the diffraction patterns were used to overcome the rapid loss of polymer crystallinity, resulting from electr on beam damage. Analysis of the diffraction patterns has shown that partial epitaxial correlation between the atomic periodicity of the particle surfa ce and the molecular periodicity of polymer chains is always present when s pherulites are nucleated. STEM images show that only large particles, with well developed facets (cleavage planes), are nucleating. The nucleating eff iciency of the filler is therefore dependent on the size as well as on the crystallographic orientation of the facet. Small particles, or those with n o suitable facets, do not affect the crystalline structure of the polymer, It is also shown that anisotropic polymer structures can be formed by inhom ogeneous dispersion of nucleating filler particles.